In conventional gas control valves used to regulate the flow of natural gas or other combustible gaseous material for home heating, and for industrial heating and drying purposes, a thermostat is provided to regulate gas flow. The thermostat typically produces an electrical signal to the gas valve to open or close the valve. Typically the signal, which is a small electric current, is passed to an electrical resistance coil that encircles the bimetallic strip. Heat generated by the coil, or the absence of such heat, causes the bimetallic strip to deflect in one direction or another. This deflective movement of the bimetallic strip operates to open or close a valve to prevent gas from flowing into or out of a gas valve housing.
The use of such gas flow control valves in association with combustible gases has been criticized to a significant extent because of the danger of an explosion within the gas valve housing. It is possible that such an explosion could spread throughout the inlet and outlet gas lines connected to the housing. If an explosive mixture of air and gas is present in a gas line, and if the electrical resistance coil is damaged or defective, a spark could result or a section of the coil could become heated to an inordinately high temperature. If this were to occur, an explosion might well result within the gas valve assembly. Moreover, such an explosion could proceed within an air-gas mixture throughout both the inlet and outlet lines to the valve housing. Furthermore, an explosion within the gas valve assembly would destroy or seriously damage the gas valve, thus causing an uncontrolled gas leak which could thereafter present an even greater major safety hazard. For these reasons, the use of electrical resistance coils, or electric heat motors as they are sometimes known, in association with gas valves for use with combustible gases has been widely suppressed.